Differences in contractile responses to electrical stimulation and alpha-adrenergic binding sites in isolated cerebral arteries of humans, cows, dogs, and monkeys.

The neurogenic responses of cerebral arteries of humans and the monkey were compared with those of the dog. alpha-Adrenoceptors in these cerebral arteries were also characterized by radioligand-binding studies. In human posterior communicating arteries, the contractile response to electrical transmural stimulation was attenuated by treatment with phentolamine in 41% of preparations tested, but not affected by aspirin. The responses in the monkey and canine arteries were not attenuated by treatment with phentolamine, but were reduced by aspirin in 60 and 73% of the cases, respectively. Reactivity and affinity to exogenous noradrenaline were comparable in human and monkey arteries, but greater than those of canine arteries. Radioligand-binding assays revealed binding sites for [3H]prazosin in the human and monkey cerebral arteries; the KD and Bmax values were not significantly different between the two species. Such binding sites were not detected in canine arteries. Binding sites for [3H]yohimbine were present in the arteries of the three species. Thus, the neurogenic contractile response of human cerebral arteries may be at least in part adrenergic in nature, while that of monkey and canine arteries may be due to neurogenically occurring arachidonate. alpha-Adrenoceptors in the monkey arteries are similar to those in humans.